I guess the old 80/20 Rule or Pareto Principle somewhat applies to the support distribution for many products. That is, 80% of the support resources are taken up by 20% of the clients. (incredibly-vaguely-speaking, naturally)

The variable is "20% of what type of client?". 20% of Taylor Swift concert attendees, or 20% of assembly coders? Each comes with its own unique challenges!